The petroleum and chemical industries have a serious problem. Namely, manufacturing processes in these industries produce large amounts of waste that is toxic and hazardous. Harmful ingredients in the waste generally do not break down over time in the environment. That is, the waste remains harmful indefinitely. Contamination of soil, air or water by small amounts of this waste can result in disastrous environmental consequences. To date, no completely satisfactory solution has been found for disposing of such waste.
One attempted solution to hazardous waste disposal has been to simply store the waste. However, the petroleum and chemical industries in the U.S. alone, produce hundreds of thousands of tons of such waste annually. Therefore, storage sites must be continuously located as previous storage sites fill. Since the waste essentially does not breakdown over time, storage sites must be carefully maintained, indefinitely, to protect against escape of the waste into the environment. In an increasingly urbanized world, clearly, a major problem with storage as a solution for disposing of hazardous waste is a lack of suitable storage space.
Another attempted solution has been the processing of hazardous waste to eliminate its harmful effects. Such processing generally involves burning hazardous waste at high temperature to reduce it to fine ash. The high temperature thoroughly oxidizes the waste and renders it nonharmful to a level suitable for disposal in a landfill. One main drawback to this solution, is that the high temperature burning generally requires significant expenditure of fossil fuels, and is thus expensive. Burning of fossil fuels also results in carbon dioxide emissions, a gas that has been increasing in accumulation in the atmosphere, and there is significant concern that the carbon dioxide accumulation will have adverse environmental impacts. Additionally, the burning typically emits other gases and pollutants that can harm the environment as well.
In the petroleum and chemical industries, manufacturing processes frequently result in hazardous wastes of crude oil and other chemical compounds contaminating tanks and other equipment. The wastes include in large part, a mixture of hydrocarbons, water, and soil particulate. The waste also typically includes metals, defined as toxic and/or hazardous under the U.S. Resource Conservation and Recovery Act ("RCRA"). Water and soil particulate usually forms the majority portion by volume in the wastes, and are bound with the hydrocarbons and metals in a gelatinous residue. In the oil and chemical industries, this residue is generally referred to as "sludge."
Attempts have been made to recycle sludge. The recycling process typically involves centrifuging the sludge to separate a liquid mixture of hydrocarbons and water, from thicker, more solid material, such as soil particulate. Known processing techniques can thereafter be applied to the liquid mixture to separate hydrocarbons from water. Separated hydrocarbons are generally recycled as a commercially valuable product. Water separated from hydrocarbons, and other contaminants, is considered to be nonhazardous, and is appropriately disposed of, i.e., sewered.
There are three main problems with recycling sludge, however. First, the processing techniques for separating hydrocarbons from water can be costly. Second, these processing techniques often involve using environmentally hazardous chemicals to separate hydrocarbons that are mixed with water. For example, U.S. Pat. No. 5,092,983 teaches using solvents, preferably n-pentane and toluene, for dissolving and separating hydrocarbons from water. Both solvents can be environmentally hazardous.
Third, and perhaps most importantly, no suitable processing techniques have been identified for removing toxic metals from sludge. More particularly, before soil particulate can be rendered nonhazardous, and appropriately disposed of, such as in a landfill, all toxic metals must be substantially removed. Metals remaining in fill soil frequently contaminate the environment due to leaching, with catastrophic environmental consequences. The difficulty in separating metals is most likely due to complex bonds that form between metals and hydrocarbons.
Rather than removing toxic metals when recycling sludge, proposals have been made to leave metals mixed with soil particulate, after treating the soil to inhibit leaching. Referring to U.S. Pat. No. 5,092,983 again, this patent teaches treating solids produced by the disclosed recycling process, with fixation chemicals to prevent leaching, rather than removing the metals. Thereafter, the treated solids are disposed of in a landfill. U.S. Pat. No. 5,269,906 discloses mixing an alkaline material (preferably calcium oxide) with sludge to reduce toxic leachability of nickel metal in the sludge, rather than removing the nickel.
While fixation techniques may inhibit leaching, there is still a significant danger of environmental contamination, especially over the long-term, from toxic metal leaching. A better solution is to ensure against environmental contamination by removing toxic metals before disposing of solid particulate.
The present invention provides an improved recycling solution for addressing the problem of hazardous waste disposal.